Multi-layer golf ball

ABSTRACT

The present invention is directed to an improved multi-layer golf ball comprising a core, an inner cover layer and an outer cover layer. The inner cover layer is comprised of a high acid ionomer or ionomer blend which may or may not include a filler such as zinc-stearate. The outer cover layer is comprised of a soft, very low modulus ionomer or ionomer blend, or a non-ionomeric thermoplastic elastomer such as polyurethane, polyester or polyesteramide. The resulting multi-layered golf ball of the present invention provides for enhanced distance without sacrificing playability or durability when compared to known multi-layer golf balls.

1. This is a divisional of application Ser. No. 08/714,661 filed on Sep.15, 1996 which, in turn, is a divisional of application Ser. No.08/562,540 filed on Nov. 20, 1995, which is a continuation ofapplication Ser. No. 08/070,510.

FIELD OF THE INVENTION

2. The present invention relates to golf balls and, more particularly,to improved golf balls comprising multi-layer coves which have a hardinner layer and a relatively soft outer layer. The improved multi-layergolf balls provide for enhanced distance and durability properties whileat the same time offering the “feel” and spin characteristics associatedwith soft balata and balata-like covers of the prior art.

BACKGROUND OF THE INVENTION

3. Traditional golf ball covers have been comprised of balata or blendsof balata with elastomeric or plastic materials. The traditional balatacovers are relatively soft and flexible. Upon impact, the soft balatacovers compress against the surface of the club producing high spin.Consequently, the soft and flexible balata covers provide an experiencedgolfer with the ability to apply a spin to control the ball in flight inorder to produce a draw or a fade, or a backspin which causes the ballto “bite” or stop abruptly on contact with the green. Moreover, the softbalata covers produce a soft “feel” to the low handicap player. Suchplayability properties (workability, feel, etc.) are particularlyimportant in short iron play with low swing speeds and are exploitedsignificantly by relatively skilled players.

4. Despite all the benefits of balata, balata covered golf balls areeasily cut and/or damaged if mis-hit. Golf balls produced with balata orbalata-containing cover compositions therefore have a relatively shortlifespan.

5. As a result of this negative property, balata and its syntheticsubstitutes, trans-polybutadiene and transpolyisoprene, have beenessentially replaced as the cover materials of choice by new covermaterials comprising ionomeric resins.

6. Ionomeric resins are polymers containing interchain ionic bonding. Asa result of their toughness, durability and flight characteristics,various ionomeric resins sold by E. I. DuPont de Nemours & Company underthe trademark “Surlyn®” and more recently, by the Exxon Corporation (seeU.S. Pat. No. 4,911,451) under the trademarks “Escor®” and the tradename “Iotek”, have become the materials of choice for the constructionof golf ball covers over the traditional “balata” (transpolyisoprene,natural or synthetic) rubbers. As stated, the softer balata covers,although exhibiting enhanced playability properties, lack the durability(cut and abrasion resistance, fatigue endurance, etc.) propertiesrequired for repetitive play.

7. Ionomeric resins are generally ionic copolymers of an olefin, such asethylene, and a metal salt of an unsaturated carboxylic acid, such asacrylic acid, methacrylic acid, or maleic acid. Metal ions, such assodium or zinc, are used to neutralize some portion of the acidic groupin the copolymer resulting in a thermoplastic elastomer exhibitingenhanced properties, i.e. durability, etc., for golf ball coverconstruction over balata. However, some of the advantages gained inincreased durability have been offset to some degree by the decreasesproduced in playability. This is because although the ionomeric resinsare very durable, they tend to be very hard when utilized for golf ballcover construction, and thus lack the degree of softness required toimpart the spin necessary to control the ball in flight. Since theionomeric resins are harder than balata, the ionomeric resin covers donot compress as much against the face of the club upon impact, therebyproducing less spin. In addition, the harder and more durable ionomericresins lack the “feel” characteristic associated with the softer balatarelated covers.

8. As a result, while there are currently more than fifty (50)commercial grades of ionomers available both from DuPont and Exxon, witha wide range of properties which vary according to the type and amountof metal cations, molecular weight, composition of the base resin (i.e.,relative content of ethylene and methacrylic and/or acrylic acid groups)and additive ingredients such as reinforcement agents, etc., a greatdeal of research continues in order to develop a golf ball covercomposition exhibiting not only the improved impact resistance andcarrying distance properties produced by the “hard” ionomeric resins,but also the playability (i.e., “spin”, “feel”, etc.) characteristicspreviously associated with the “soft” balata coves, properties which arestill desired by the more skilled golfer.

9. Consequently, a number of two-piece (a solid resilient center or corewith a molded cover) and three-piece (a liquid or solid center,elastomeric winding about the center, and a molded cover) golf ballshave been produced by the present inventor and others to address theseneeds. The different types of materials utilized to formulate the cores,covers, etc. of these balls dramatically alters the balls' overallcharacteristics. In addition, multi-layered covers containing one ormore ionomer resins have also been formulated in an attempt to produce agolf ball having the overall distance, playability and durabilitycharacteristics desired.

10. This was addressed by Spalding & Evenflo Companies, Inc., theassignee of the present invention, in U.S. Pat. No. 4,431,193 where amulti-layered golf ball is disclosed. In the '193 patent, a multi-layergolf ball is produced by initially molding a first cover layer on aspherical core and then adding a second layer. The first layer iscomprised of a hard, high flexural modulus resinous material such astype 1605 Surlyn® (now designated Surlyn® 8940). Type 1605 Surlyn®(Surlyn® 8940) is a sodium ion based low acid (less than or equal to 15weight percent methacrylic acid) ionomer resin having a flexural modulusof about 51,000 psi. An outer layer of a comparatively soft, lowflexural modulus resinous material such as type 1855 Surlyn® (nowdesignated Surlyn® 9020) is molded over the inner cover layer. Type 1855Surlyn® (Surlyn® 9020) is a zinc ion based low acid (10 weight percentmethacrylic acid) ionomer resin having a flexural modulus of about14,000 psi.

11. The '193 patent teaches that the hard, high flexural modulus resinwhich comprises the first layer provides for a gain in coefficient ofrestitution over the coefficient of restitution of the core. Theincrease in the coefficient of restitution provides a ball which servesto attain or approach the maximum initial velocity limit of 255 feet persecond as provided by the United States Golf Association (U.S.G.A.)rules. The relatively soft, low flexural modulus outer layer providesessentially no gain in the coefficient of restitution but provides forthe advantageous “feel” and playing characteristics of a balata coveredgolf ball. Unfortunately, however, while a ball of the '193 patent doesexhibit enhanced playability characteristics with improved distance(i.e. enhanced C.O.R. values) over a number of other known multi-layeredballs, the ball suffers from poor cut resistance and relatively shortdistance (i.e. lower C.O.R. values) when compared to two-piece, singlecover layer balls. These undesirable properties make the ball producedin accordance with the '193 patent unacceptable by today's standards.

12. The present invention is directed to new multi-layer golf ballcompositions which provide for enhanced coefficient of restitution(i.e., enhanced resilience or carrying distance) and/or durabilityproperties when compared to the multi-layer balls found in the priorart, as well as improved outer cover layer softness and durability. Assuch, the playability characteristics (i.e., “feel”, “click”, “spin”,etc.) are not diminished.

13. These and other objects and features of the invention will beapparent from the following summary and description of the invention,the drawings and from the claims.

SUMMARY OF THE INVENTION

14. The present invention is directed to improved multi-layer golf ballcover compositions and the resulting multi-layer golf balls producedusing the improved compositions. The novel multi-layer golf ball coversof the present invention include a first or inner layer or ply of a highacid (greater than 16 weight percent acid) ionomer or ionomer blend andsecond or outer layer or ply comprised of a comparatively softer, lowmodulus ionomer, ionomer blend or other non-ionomeric thermoplasticelastomer such as polyurethane, a polyester elastomer such as Hytrel®polyester elastomer of E. I. DuPont de Nemours & Company, or apolyesteramide such as the Elf Atochem S. A. Pebax® polyesteramide.Preferably, the outer cover layer includes a blend of hard and soft lowacid (i.e. 16 weight percent acid or less) ionomers.

15. It has been found that the recently developed high acid ionomerbased inner layer, provides for a substantial increase in resilience(i.e., enhanced distance) over known multi-layer covered balls. Thesofter outer layer provides for desirable “feel” and high spin ratewhile maintaining respectable resilience. The soft outer layer allowsthe cover to deform more during impact and increases the area of contactbetween the club face and the cover, thereby imparting more spin on theball. As a result, the soft cover provides the ball with a balata-likefeel and playability characteristics with improved distance anddurability. Consequently, the overall combination of the inner and outercover layers results in a golf ball having enhanced resilience (improvedtravel distance) and durability (i.e. cut resistance, etc.)characteristics while maintaining and in many instances, improving theballs playability properties.

16. The combination of a high acid ionomer or ionomer blend inner coverlayer with a soft, relatively low modulus ionomer, ionomer blend orother non-ionomeric thermoplastic elastomer outer cover layer providesfor excellent overall coefficient of restitution (i.e., excellentresilience) because of the improved resiliency produced by the innercover layer. While some improvement in resilience is also produced bythe outer cover layer, the outer cover layer generally provides for amore desirable feel and high spin, particularly at lower swing speedswith highly lofted clubs such as half wedge shots.

17. Two principal properties involved in golf ball performance arearesilience and hardness. Resilience is determined by the coefficient ofrestitution (C.O.R.), the constant “e” which is the ratio of therelative velocity of two elastic spheres after direct impact to thatbefore impact. As a result, the coefficient of restitution (“e”) canvary from 0 to 1, with 1 being equivalent to an elastic collision and 0being equivalent to an inelastic collision.

18. Resilience (C.O.R.), along with additional factors such as club headspeed, angle of trajectory and ball configuration (i.e., dimple pattern)generally determine the distance a ball will travel when hit. Since clubhead speed and the angle of trajectory are factors not easilycontrollable by a manufacturer, factors of concern among manufacturersare the coefficient of restitution (C.O.R.) and the surfaceconfiguration of the ball.

19. The coefficient of restitution (C.O.R.) in solid core balls is afunction of the composition of the molded core and of the cover. Inballs containing a wound core (i.e., balls comprising a liquid or solidcenter, elastic windings, and a cover), the coefficient of restitutionis a function of not only the composition of the center and cover, butalso the composition and tension of the elastomeric windings. Althoughboth the core and the cover contribute to the coefficient ofrestitution, the present invention is directed to the enhancedcoefficient of restitution (and thus travel distance) which is affectedby the cover composition.

20. In this regard, the coefficient of restitution of a golf ball isgenerally measured by propelling a ball at a given speed against a hardsurface and measuring the ball's incoming and outgoing velocityelectronically. As mentioned above, the coefficient of restitution isthe ratio of the outgoing velocity to the incoming velocity. Thecoefficient of restitution must be carefully controlled in allcommercial golf balls in order for the ball to be within thespecifications regulated by the United States Golf Association(U.S.G.A.). Along this line, the U.S.G.A. standard indicate that a“regulation” ball cannot have an initial velocity (i.e., the speed offthe club) exceeding 255 feet per second. Since the coefficient ofrestitution of a ball is related to the ball's initial velocity, it ishighly desirable to produce a ball having sufficiently high coefficientof restitution to closely approach the U.S.G.A. limit on initialvelocity, while having an ample degree of softness (i.e., hardness) toproduce enhanced playability (i.e., spin, etc.).

21. The hardness of the ball is the second principal property involvedin the performance of a golf ball. The hardness of the ball can affectthe playability of the ball on striking and the sound or “click”produced. Hardness is determined by the deformation (i.e., compression)of the ball under various load conditions applied across the ball'sdiameter (i.e., the lower the compression value, the harder thematerial). As indicated in U.S. Pat. No. 4,674,751, softer covers permitthe accomplished golfer to impart proper spin. This is because thesofter covers deform on impact significantly more than balls having“harder” ionomeric resin covers. As a result, the better player isallowed to impart fade, draw or backspin to the ball thereby enhancingplayability. Such properties may be determined by various spin ratetests such as the “nine ion” spin rate test described below in theExamples.

22. Accordingly, the present invention is directed to an improvedmulti-layer cover which produces, upon molding each layer around a core(preferably a solid core) to formulate a multi-layer cover, a golf ballexhibiting enhanced distance (i.e., resilience) without adverselyaffecting, and in many instances, improving the ball's playability(hardness/softness) and/or durability (i.e., cut resistance, fatigueresistance, etc.) characteristics.

23. These and other objects and features of the invention will beapparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

24.FIG. 1 is a cross-sectional view of a golf ball embodying theinvention illustrating a core 10 and a cover 12 consisting of an innerlayer 14 and an outer layer 16 having dimples 18; and

25.FIG. 2 is a diametrical cross-sectional view of a golf ball of theinvention having a core 10 and a cover 12 made of an inner layer 14 andan outer layer 16 having dimple 18.

DETAILED DESCRIPTION OF THE INVENTION

26. The present invention relates to improved multi-layer golf balls,particularly a golf ball comprising a multi-layered cover 12 over asolid core 10, and method for making same.

27. The multi-layered cover 12 comprises two layers: a first or innerlayer or ply 14 and a second or outer layer or ply 16. The inner layer14 is comprised of a high acid (i.e. greater than 16 weight percentacid) ionomer resin or high acid ionomer blend. Preferably, the innerlayer is comprised of a blend of two or more high acid (i.e. at least 16weight percent acid) ionomer resin neutralized to various extents bydifferent metal cations. The inner core layer may or may not include ametal stearate (e.g., zinc stearate) or other metal fatty acid salt. Thepurpose of the metal stearate or other metal fatty acid salt is to lowerthe cost of production without affecting the overall performance of thefinished golf ball.

28. The inner layer compositions include the high acid ionomers such asthose recently developed by E. I. DuPont de Nemours & Company under thetrademark “Surlyn®” and by Exxon Corporation under the trademark“Escor®” or tradename “Iotek”, or blends thereof. Examples ofcompositions which may be used as the inner layer herein are set forthin detail in copending U.S. Ser. No. 07/776,803 filed Oct. 15, 1991, andSer. No. 07/901,660 filed Jun. 19, 1992, both incorporated herein byreference. Of course, the inner layer high acid ionomer compositions arenot limited in any way to those compositions set forth in said copendingapplications. For example, the high acid ionomer resins recentlydeveloped by Spalding & Evenflo Companies, Inc., the assignee of thepresent invention, and disclosed in U.S. Ser. No. 07/901,680, filed Jun.19, 1992, incorporated herein by reference, may also be utilized toproduce the inner layer of the multi-layer cover used in the presentinvention.

29. The high acid ionomers which may be suitable for use in formulatingthe inner layer compositions of the subject invention are ioniccopolymers which are the metal, i.e., sodium, zinc, magnesium, etc.,salts of the reaction product of an olefin having from about 2 to 8carbon atoms and an unsaturated monocarboxylic acid having from about 3to 8 carbon atoms. Preferably, the ionomeric resins are copolymers ofethylene and either acrylic or methacrylic acid. In some circumstances,an additional comonomer such as an acrylate ester (i.e., iso- orn-butylacrylate, etc.) can also be included to produce a softerterpolymer. The carboxylic acid groups of the copolymer are partiallyneutralized (i.e., approximately 10-75%, preferably 30-70%) by the metalions. Each of the high acid ionomer resins which may be included in theinner layer cover compositions of the invention contains greater thanabout 16% by weight of a carboxylic acid, preferably from about 17% toabout 25% by weight of a carboxylic acid, more preferably from about18.5% to about 21.5% by weight of a carboxylic acid.

30. Although the inner layer cover composition preferably includes ahigh acid ionomeric resin and the scope of the patent embraces all knownhigh acid ionomeric resins falling within the parameters set forthabove, only a relatively limited number of these high acid ionomericresins have recently become commercially available.

31. The high acid ionomeric resins available from Exxon under thedesignation “Escor®” and or “Iotek”, are somewhat similar to the highacid ionomeric resins available under the “Surlyn®” trademark. However,since the Escor®/Iotek ionomeric resins are sodium or zinc salts ofpoly(ethylene-acrylic acid) and the “Surlyn®” resins are zinc, sodium,magnesium, etc. salts of poly(ethylene-methacrylic acid), distinctdifferences in properties exist.

32. Examples of the high acid methacrylic acid based ionomers foundsuitable for use in accordance with this invention include Surlyn®Ad-8422 (sodium cation), Surlyn® 8162 (zinc cation), Surlyn® SEP-503-1(zinc cation), and Surlyn® SEP-503-2 (magnesium cation). According toDuPont, all of these ionomers contain from about 18.5 to about 21.5% byweight methacrylic acid.

33. More particularly, Surlyn® AD-8422 is currently commerciallyavailable from DuPont in a number of different grades (i.e., AD-8422-2,AD-8422-3, AD-8422-5, etc.) based upon differences in melt index.According to DuPont, Surlyn® AD-8422 offers the following generalproperties when compared to Surlyn®8920, the stiffest, hardest of all onthe low acid grades (referred to as “hard” ionomers in U.S. Pat. No.4,884,814): LOW ACID HIGH ACID (15 wt % Acid) (>20 wt % Acid) SURLYN ®SURLYN ® SURLYN ® 8920 8422-2 8422-3 IONOMER Cation Na Na Na Melt Index1.2 2.8 1.0 Sodium, Wt % 2.3 1.9 2.4 Base Resin MI 60 60 60 MP¹, ° C. 8886 85 FP¹, ° C. 47 48.5 45 COMPRESSION MOLDING² Tensile Break, psi 43504190 5330 Yield, psi 2880 3670 3590 Elongation, % 315 263 289 Flex Mod,K psi 53.2 76.4 88.3 Shore D hardness 66 67 68

34. In comparing Surlyn® 8920 to Surlyn® 8422-2 and Surlyn® 8422-3, itis noted that the high acid Surlyn® 8422-2 and 8422-3 ionomers have ahigher tensile yield, lower elongation, slightly higher Short D hardnessand much higher flexural modulus. Surlyn® 8920 contains 15 weightpercent methacrylic acid and is 59% neutralized with sodium.

35. In addition, Surlyn® SEP-503-1 (zinc cation) and Surlyn® SEP-503-2(magnesium cation) are high acid zinc and magnesium versions of theSurlyn® AD 8422 high acid ionomers. When compared to the Surlyn® AD 8422high acid ionomers, the Surlyn SEP-503-1 and SEP-503-2 ionomers can bedefined as follows: Surlyn ® Ionomer Ion Melt Index Neutralization % AD8422-3  Na 1.0 45 SEP 503-1 Zn 0.8 38 SEP 503-2 Mg 1.8 43

36. Furthermore, Surlyn® 8162 is a zinc cation ionomer resin containingapproximately 20% by weight (i.e. 18.5-21.5% weight) methacrylic acidcopolymer that has been 30-70% neutralized. Surlyn® 8162 is currentlycommercially available from DuPont.

37. Examples of the high acid acrylic acid based ionomers suitable foruse in the present invention also include the Escor® or Iotek high acidethylene acrylic acid ionomers produced by Exxon. In this regard, Escor®or Iotek 959 is a sodium ion neutralized ethylene-acrylic neutralizedethylene-acrylic acid copolymer. According to Exxon, Ioteks 959 and 960contain from about 19.0 to about 21.0% by weight acrylic acid withapproximately 30 to about 70 percent of the acid groups neutralized withsodium and zinc ions, respectively. The physical properties of thesehigh acid acrylic acid based ionomers are as follows: ESCOR ® PROPERTYESCOR ® (IOTEK) 959 (IOTEK) 960 Melt Index, g/10 min 2.0 1.8 CationSodium Zinc Melting Point, ° F. 172 174 Vicat Softening Point, ° F. 130131 Tensile @ Break, psi 4600 3500 Elongation @ Break, % 325 430Hardness, Shore D 66 57 Flexural Modulus, psi 66,000 27,000

38. Furthermore, as a result of the development by the inventor of anumber of new high acid ionomers neutralized to various extents byseveral different types of metal cations, such as by manganese, lithium,potassium, calcium and nickel cations, several new high acid ionomersand/or high acid ionomer blends besides sodium, zinc and magnesium highacid ionomers or ionomer blends are now available for gold ball coverproduction. It has been found that these new cation neutralized highacid ionomer blends produce inner cover layer compositions exhibitingenhanced hardness and resilience due to synergies which occur duringprocessing. Consequently, the metal cation neutralized high acid ionomerresins recently produced can be blended to produce substantially harderinner cover layers for multi-layered golf balls having higher C.O.R.'sthan those produced by the low acid ionomer inner cover compositionspresently commercially available.

39. More particularly, several new metal cation neutralized high acidionomer resins have been produced by the inventor by neutralizing, tovarious extents, high acid copolymers of an alpha-olefin and an alpha,beta-unsaturated carboxylic acid with a wide variety of different metalcation salts. This discovery is the subject matter of U.S. applicationSer. No. 901,680, incorporated herein by reference. It has been foundthat numerous new metal cation neutralized high acid ionomer resins canbe obtained by reacting a high acid copolymer (i.e. a copolymercontaining greater than 16% by weight acid, preferably from about 17 toabout 25 weight percent acid, and more preferably about 20 weightpercent acid), with a metal cation salt capable of ionizing orneutralizing the copolymer to the extent desired (i.e. from about 10% to90%).

40. The base copolymer is made up of greater than 16% by weight of analpha, beta-unsaturated carboxylic acid and an alpha-olefin. Optionally,a softening comonomer can be included in the copolymer. Generally, thealpha-olefin has from 2 to 10 carbon atoms and is preferably ethylene,and the unsaturated carboxylic acid is a carboxylic acid having fromabout 3 to 8 carbons. Examples of such acids include acrylic acid,methacrylic acid, ethacrylic acid, chloroacrylic acid, crotonic acid,maleic acid, fumaric acid, and itaconic acid, with acrylic acid beingpreferred.

41. The softening comonomer that can be optionally included in theinvention may be selected from the group consisting of vinyl esters ofaliphatic carboxylic acids wherein the acids have 2 to 10 carbon atoms,vinyl ethers wherein the alkyl groups contains 1 to 10 carbon atoms, andalkyl acrylates or methacrylates wherein the alkyl group contains 1 to10 carbon atoms. Suitable softening comonomers include vinyl acetate,methyl acrylate, methyl methacrylate, ethyl acrylate, ethylmethacrylate, butyl acrylate, butyl methacrylate, or the like.

42. Consequently, examples of a number of copolymers suitable for use toproduce the high acid ionomers included in the present inventioninclude, but are not limited to, high acid embodiments of anethylene/acrylic acid copolymer, an ethylene/methacrylic acid copolymer,an ethylene/itaconic acid copolymer, an ethylene/maleic acid copolymer,an ethylene/methacrylic acid/vinyl acetate copolymer, anethylene/acrylic acid/vinyl alcohol copolymer, etc. The base copolymerbroadly contains greater than 16% by weight unsaturated carboxylic acid,from about 30 to about 83% by weight ethylene and from 0 to about 40% byweight of a softening comonomer. Preferably, the copolymer containsabout 20% by weight unsaturated carboxylic acid and about 80% by weightethylene. Most preferably, the copolymer contains about 20% acrylic acidwith the remainder being ethylene.

43. Along these lines, examples of the preferred high acid basecopolymers which fulfill the criteria set forth above, are a series ofethylene-acrylic copolymers which are commercially available from TheDown Chemical Company, Midland, Mich., under the “Primacor” designation.These high acid base copolymers exhibit the typical properties set forthbelow in Table 1. TABLE 1 Typical Properties of PrimacorEthylene-Acrylic Acid Copolymers MELT TENSILE FLEXURAL VICAT PERCENTDENSITY, INDEX, YD. ST MODULUS SOFT PT SHORE D GRADE ACID glcc g/10 min(psi) (psi) (° C.) HARDNESS ASTM D-792 D-1238 D-638 D-790 D-1525 D-22405980 20.0 0.958 300.0 — 4800 43 50 5990 20.0 0.955 1300.0  650 2600 4042 5990 20.0 0.955 1300.0  650 3200 40 42 5981 20.0 0.960 300.0 900 320046 48 5981 20.0 0.960 300.0 900 3200 46 48 5983 20.0 0.958 500.0 8503100 44 45 5991 20.0 0.953 2600.0  635 2600 38 40

44. Due to the high molecular weight of the Primacor 5981 grade of theethylene-acrylic acid copolymer, this copolymer is the more preferredgrade utilized in the invention.

45. The metal cation salts utilized in the invention are those saltswhich provide the metal cations capable of neutralizing, to variousextents, the carboxylic acid groups of the high acid copolymer. Theseinclude acetate, oxide or hydroxide salts of lithium, calcium, zinc,sodium, potassium, nickel, magnesium, and manganese.

46. Examples of such lithium ion sources are lithium hydroxidemonohydrate, lithium hydroxide, lithium oxide and lithium acetate.Sources for the calcium ion include calcium hydroxide, calcium acetateand calcium oxide. Suitable zinc ion sources are zinc acetate dihydrateand zinc acetate, a blend of zinc oxide and acetic acid. Examples ofsodium ion sources are sodium hydroxide and sodium acetate. Sources forthe potassium ion include potassium hydroxide and potassium acetate.Suitable nickel ion sources are nickel acetate, nickel oxide and nickelhydroxide. Sources of magnesium include magnesium oxide, magnesiumhydroxide, magnesium acetate. Sources of manganese include manganeseacetate and manganese oxide.

47. The new metal cation neutralized high acid ionomer resins areproduced by reacting the high acid base copolymer with various amountsof the metal cation salts above the crystalline melting point of thecopolymer, such as at a temperature from about 200° F. to about 500° F.,preferably from about 250° F. to about 350° F. under high shearconditions at a pressure of from about 10 psi to 10,000 psi. Other wellknown blending techniques may also be used. The amount of metal cationsalt utilized to produce the new metal cation neutralized high acidbased ionomer resins is the quantity which provides a sufficient amountof the metal cations to neutralize the desired percentage of thecarboxylic acid groups in the high acid copolymer. The extent ofneutralization is generally from about 10% to about 90%.

48. As indicated below in Table 2 and more specifically in Example 1 inU.S. application Ser. No. 901,680, a number of new types of metal cationneutralized high acid ionomers can be obtained from the above indicatedprocess. These include new high acid ionomer resins neutralized tovarious extents with manganese, lithium, potassium, calcium and nickelcations. In addition, when a high acid ethylene/acrylic acid copolymeris utilized as the base copolymer component of the invention and thiscomponent is subsequently neutralized to various extents with the metalcation salts producing acrylic acid based high acid ionomer resinsneutralized with cations such as sodium, potassium, lithium, zinc,magnesium, manganese, calcium and nickel, several new cation neutralizedacrylic acid based high acid ionomer resins are produced. TABLE 2Formulation Wt-% Wt-% Melt Shore D No. Cation Salt Neutralization IndexC.O.R. Hardness 1(NaOH) 6.98 67.5 0.9 .804 71 2(NaOH) 5.66 54.0 2.4 .80873 3(NaOH) 3.84 35.9 12.2 .812 69 4(NaOH) 2.91 27.0 17.5 .812 (brittle)5(MnAc) 19.6 71.7 7.5 .809 73 6(MnAc) 23.1 88.3 3.5 .814 77 7(MnAc) 15.353.0 7.5 .810 72 8(MnAc) 26.5 106 0.7 .813 (brittle) 9(LiOH) 4.54 71.30.6 .810 74 10(LiOH) 3.38 52.5 4.2 .818 72 11(LiOH) 2.34 35.9 18.6 .81572 12(KOH) 5.30 36.0 19.3 Broke 70 13(KOH) 8.26 57.9 7.18 .804 7014(KOH) 10.7 77.0 4.3 .801 67 15(ZnAc) 17.9 71.5 0.2 .806 71 16(ZnAc)13.9 53.0 0.9 .797 69 17(ZnAc) 9.91 36.1 3.4 .793 67 18(MgAc) 17.4 70.72.8 .814 74 19(MgAc) 20.6 87.1 1.5 .815 76 20(MgAc) 13.8 53.8 4.1 .81474 21(CaAc) 13.2 69.2 1.1 .813 74 22(CaAc) 7.12 34.9 10.1 .808 70Controls: 50/50 Blend of Ioteks 8000/7030 C.O.R. = .810/65 Shore DHardness Dupont High Acid Surlyn ® 8422 (Na) C.O.R. = .811/70 Shore DHardness DuPont High Acid Surlyn ® 8162 (Zn) C.O.R. = .807/65 Shore DHardness Exxon High Acid Iotek EX-960 (Zn) C.O.R. = .796/65 Shore DHardness 23(MgO) 2.91 53.5 2.5 .813 24(MgO) 3.85 71.5 2.8 .808 25(MgO)4.76 89.3 1.1 .809 26(MgO) 1.96 35.7 7.5 .815 Control for Formulations23-26 is 50/50 Iotek 8000/7030, C.O.R. = .814, Formulation 26 C.O.R. wasnormalized to that control accordingly 27(NiAc) 13.04 61.1 0.2 .802 7128(NiAc) 10.71 48.9 0.5 .799 72 29(NiAc) 8.26 36.7 1.8 .796 69 30(NiAc)5.66 24.4 7.5 .786 64 Control for Formulation Nos. 27-30 is 50/50 Iotek8000/7030, C.O.R. = .807

49. When compared to low acid versions of similar cation neutralizedionomer resins, the new metal cation neutralized high acid ionomerresins exhibit enhanced hardness, modulus and resiliencecharacteristics. These are properties that are particularly desirable ina number of thermoplastic fields, including the field of golf ballmanufacturing.

50. When utilized in the construction of the inner layer of amulti-layered golf ball, it has been found that the new acrylic acidbased high acid ionomers extend the range of hardness beyond thatpreviously obtainable while maintaining the beneficial properties (i.e.durability, click, feel, etc.) of the softer low acid ionomer coveredballs, such as balls produced utilizing the low acid ionomers disclosedin U.S. Pat. Nos. 4,884,814 and 4,911,451.

51. Moreover, as a result of the development of a number of new acrylicacid based high acid ionomer resins neutralized to various extents byseveral different types of metal cations, such as manganese, lithium,potassium, calcium and nickel cations, several new ionomers or ionomerblends are now available for production of an inner cover layer of amulti-layered golf ball. By using these high acid ionomer resins,harder, stiffer inner cover layers having higher C.O.R.s, and thuslonger distance, can be obtained.

52. More preferably, it has been found that when two or more of theabove-indicated high acid ionomers, particularly blends of sodium andzinc high acid ionomers, are processed to produce the covers ofmulti-layered golf balls, (i.e., the inner cover layer herein) theresulting golf balls will travel further than previously knownmulti-layered golf balls produced with low acid ionomer resin covers dueto the balls' enhanced coefficient of restitution values.

53. For example, the multi-layer golf ball taught in 4,650,193 does notincorporate a high acid ionomeric resin in the inner cover layer. Aswill be set forth below in the Examples, the coefficient of restitutionof the golf ball having an inner layer taught by the '193 patent (i.e.,inner layer composition “D” in the Examples) is substantially lower thanthe coefficient of restitution of the remaining compositions. Inaddition, the multi-layered ball disclosed in the '193 patent sufferssubstantially in durability in comparison with the present invention.

54. With respect to the outer layer 16 of the multi-layered cover of thepresent invention, the outer cover layer is comparatively softer thanthe high acid ionomer based inner layer. The softness provides for thefeel and playability characteristics typically associated with balata orbalata-blend balls. The outer layer or ply is comprised of a relativelysoft, low modulus (about 1,000 psi to about 10,000 psi) and low acid(less than 16 weight percent acid) ionomer, ionomer blend or anon-ionomeric thermoplastic elastomer such as, but not limited to, apolyurethane, a polyester elastomer such as that marketed by DuPontunder the trademark Hytrel®, or a polyester amide such as that marketedby Elf Atochem S. A. under the trademark Pebax®. The outer layer isfairly thin (i.e. from about 0.010 to about 0.050 in thickness, moredesirably 0.03 inches in thickness for a 1.680 inch ball), but thickenough to achieve desired playability characteristics while minimizingexpense.

55. Preferably, the outer layer includes a blend of hard and soft (lowacid) ionomer resins such as those described in U.S. Pat. Nos. 4,884,814and 5,120,791, both incorporated herein by reference. Specifically, adesirable material for use in molding the outer layer comprises a blendof a high modulus (hard) ionomer with a low modulus (soft) ionomer toform a base ionomer mixture. A high modulus ionomer herein is one whichmeasures from about 15,000 to about 70,000 psi as measured in accordancewith ASTM method D-790. The hardness may be defined as at least 50 onthe Shore D scale as measured in accordance with ASTM method D-2240.

56. A low modulus ionomer suitable for use in the outer layer blend hasa flexural modulus measuring from about 1,000 to about 10,000 psi, witha hardness of about 20 to about 40 on the Shore D scale.

57. The hard ionomer resins utilized to produce the outer cover layercomposition hard/soft blends include ionic copolymers which are thesodium, zinc, magnesium or lithium salts of the reaction product of anolefin having from 2 to 8 carbon atoms and an unsaturated monocarboxylicacid having from 3 to 8 carbon atoms. The carboxylic acid groups of thecopolymer may be totally or partially (i.e. approximately 15-75 percent)neutralized.

58. The hard ionomeric resins are likely copolymers of ethylene andeither acrylic and/or methacrylic acid, with copolymers of ethylene andacrylic acid being the most preferred. Two or more types of hardionomeric resins may be blended into the outer cover layer compositionsin order to produce the desired properties of the resulting golf balls.

59. As discussed earlier herein, the hard ionomeric resins introducedunder the designation Escor® and sold under the designation “Iotek” aresomewhat similar to the hard ionomeric resins sold under the Surlyn®trademark. However, since the “Iotek” ionomeric resins are sodium orzinc salts of poly(ethylene-acrylic acid) and the Surlyn®resins are zincor sodium salts of poly(ethylene-methacrylic acid) some distinctdifferences in properties exist. As more specifically indicated in thedata set forth below, the hard “Iotek” resins (i.e., the acrylic acidbased hard ionomer resins) are the more preferred hard resins for use informulating the outer layer blends for use in the present invention. Inaddition, various blends of “Iotek” and Surlyn® hard ionomeric resins,as well as other available ionomeric resins, may be utilized in thepresent invention in a similar manner.

60. Examples of commercially available hard ionomeric resins which maybe used in the present invention in formulating the outer cover blendsinclude the hard sodium ionic copolymer solid under the trademarkSurlyn®8940 and the hard zinc ionic copolymer sold under the trademarkSurlyn®9910. Surlyn®9040 is a copolymer of ethylene with methacrylicacid and about 15 weight percent acid which is about 29 percentneutralized with sodium ions. This resin has an average melt flow indexof about 2.8 Surlyn®9910 is a copolymer of ethylene and methacrylic acidwith about 15 weight percent acid which is about 58 percent neutralizedwith zinc ions. The average melt flow index of Surlyn®9910 is about 0.7.The typical properties of Surlyn®9910 and 8940 are set forth below inTable 3: TABLE 3 Typical Properties of Commercially Available HardSurlyn ® Resins Suitable for Use in the Outer Layer Blends of thePresent Invention ASTM D 8940 9910 8920 8528 9970 9730 Cation TypeSodium Zinc Sodium Sodium Zinc Zinc Melt flow index, D-1238 2.8 0.7 0.91.3 14.0 1.6 gms/10 min. Specific Gravity, D-792 0.95 0.97 0.95 0.940.95 0.95 g/cm³ Hardness, Shore D D-2240 66 64 66 60 62 63 TensileStrength, D-638 (4.8) (3.6) (5.4) (4.2) (3.2) (4.1) (kpsi), MPa 33.124.8 37.2 29.0 22.0 28.0 Elongation, % D-638 470 290 350 450 460 460Flexural Modulus, D-790  (51)  (48)  (55)  (32)  (28)  (30) (kpsi) MPa350 330 380 220 190 210 Tensile Impact (23° C.) D-1822S 1020 1020 8651160 760 1240 KJ/m₂ (ft.-lbs./in²) (485) (485) (410) (550) (360) (590)Vicat Temperature, ° C. D-1525 63 62 58 73 61 73

61. Examples of the more pertinent acrylic acid based hard ionomer resinsuitable for use in the present outer cover composition sold under the“Iotek” tradename by the Exxon Corporation include Iotek 4000, Iotek4010, Iotek 8000, Iotek 8020 and Iotek 8030. The typical properties ofthese and other Iotek hard ionomers suited for use in formulating theouter layer cover composition are set forth below in Table 4: TABLE 4Typical Properties of Iotek Ionomers ASTM Method Units 4000 4010 80008020 8030 Resin Properties Cation type zinc zinc sodium sodium sodiumMelt index D-1238 g/10 min. 2.5 1.5 0.8 1.6 2.8 Density D-1505 kg/m³ 963963 954 960 960 Melting Point D-3417 ° C. 90 90 90 87.5 87.5Crystallization Point D-3417 ° C. 62 64 56 53 55 Vicat Softening PointD-1525 ° C. 62 63 61 64 67 % Weight Acrylic Acid 16 11 % of Acid Groups30 40 cation neutralized Plaque Properties (3 mm thick, compressionmolded) Tensile at break D-638 MPa 24 26 36 31.5 28 Yield point D-638MPa none none 21 21 23 Elongation at break D-638 % 395 420 350 410 3951% Secant modulus D-638 MPa 160 160 300 350 390 Shore Hardness D D-2240— 55 55 61 58 59 Film Properties (50 micron film 2.2:1 Blow-up ratio)Tensile at Break MD D-882 MPa 41 39 42 52 47.4 TD D-882 MPa 37 38 38 3840.5 Yield point MD D-882 MPa 15 17 17 23 21.6 TD D-882 MPa 14 15 15 2120.7 Elongation at Break MD D-882 % 310 270 260 295 305 TD D-882 % 360340 280 340 345 1% Secant modulus MD D-882 MPa 210 215 390 380 380 TDD-882 MPa 200 225 380 350 345 Dart Drop Impact D-1709 g/micron 12.4 12.520.3 ASTM Method Units 7010 7020 7030 Resin Properties Cation type zinczinc zinc Melt Index D-1238 g/10 min. 0.8 1.5 2.5 Density D-1505 kg/m³960 960 960 Melting Point D-3417 ° C. 90 90 90 Crystallization D-3417 °C. — — — Point Vicat Softening D-1525 ° C. 60 63 62.5 Point % WeightAcrylic Acid — — — % of Acid Groups — — — Cation Neutralized PlaqueProperties (3 mm thick, compression molded) Tensile at break D-638 MPa38 38 38 Yield Point D-638 MPa none none none Elongation at break D-638% 500 420 395 1% Secant modulus D-638 MPa — — — Shore Hardness D D-2240— 57 55 55

62. Comparatively, soft ionomers are used in formulating the hard/softblends of the outer cover composition. These ionomers include acrylicacid based soft ionomers. They are generally characterized as comprisingsodium or zinc salts of a terpolymer of an olefin having from about 2 to8 carbon atoms, acrylic acid, and an unsaturated monomer of the acrylateester class having from 1 to 21 carbon atoms. The soft ionomer ispreferably a zinc based ionomer made from an acrylic acid base polymerin an unsaturated monomer of the acrylate ester class. The soft (lowmodulus) ionomers have a hardness from about 20 to about 40 as measuredon the Shore D scale and a flexural modulus from about 1,000 to about10,000, as measured in accordance with ASTM method D-790.

63. Certain ethylene-acrylic acid based soft ionomer resins developed bythe Exxon Corporation under the designation “Iotek 7520” (referred toexperimentally by differences in neutralization and melt indexes as LDX195, LDX 196, LDX 218 and LDX 219) may be combined with known hardionomers such as those indicated above to produce the outer cover. Thecombination produces higher C.O.R.s at equal or softer hardness, highermelt flow (which corresponds to improved, more efficient molding, i.e.,fewer rejects) as well as significant cost savings versus the outerlayer of multi-layer balls produced by other known hard-soft ionomerblends as a result of the lower overall raw materials costs and improvedyields.

64. While the exact chemical composition of the resins to be sold byExxon under the designation Iotek 7520 is considered by Exxon to beconfidential and proprietary information, Exxon's experimental productdata sheet lists the following physical properties of the ethyleneacrylic acid zinc ionomer developed by Exxon: TABLE 5 Property ASTMMethod Units Typical Value Physical Properties of Iotek 7520 Melt IndexD-1238 g/10 min. 2 Density D-1505 kg/m³ 0.962 Cation Zinc Melting PointD-3417 ° C. 66 Crystallization Point D-3417 ° C. 49 Vicat SofteningPoint D-1525 ° C. 42 Plaque Properties (2 mm thick Compression MoldedPlaques) Tensile at Break D-638 MPa 10 Yield Point D-638 MPa NoneElongation at Break D-638 % 760 1% Secant Modulus D-638 MPa 22 Shore DHardness D-2240 32 Flexural Modulus D-790 MPa 26 Zwick Rebond ISO 4862 %52 De Mattia Flex D-430 Cycles >5000 Resistance

65. In addition, test data collected by the inventor indicates thatIotek 7520 resins have Shore D hardnesses of about 32 to 36 (per ASTMD-2240), melt flow indexes of 3±0.5 g/10 min (at 190° C. per ASTMD-1288), and a flexural modulus of about 2500-3500 psi (per ASTM D-790).Furthermore, testing by an independent testing laboratory by pyrolysismass spectrometry indicates that Iotek 7520 resins are generally zincsalts of a terpolymer of ethylene, acrylic acid, and methyl acrylate.

66. Furthermore, the inventor has found that a newly developed grade ofan acrylic acid based soft ionomer available from the Exxon Corporationunder the designation Iotek 7510, is also effective, when combined withthe hard ionomers indicated above in producing golf ball coversexhibiting higher C.O.R. values at equal or softer hardness than thoseproduced by known hard-soft ionomer blends. In this regard, Iotek 7510has the advantages (i.e. improved flow, higher C.O.R. values at equalhardness, increased clarity, etc.) produced by the Iotek 7520 resin whencompared to the methacrylic acid base soft ionomers known in the art(such as the Surlyn 8625 and the Surlyn 8629 combinations disclosed inU.S. Pat. No. 4,884,814).

67. In addition, Iotek 7510, when compared to Iotek 7520, producesslightly higher C.O.R. valves at equal softness/hardness due to theIotek 7510's higher hardness and neutralization. Similarly, Iotek 7510produces better release properties (from the mold cavities) due to itssightly higher stiffness and lower flow rate than Iotek 7520. This isimportant in production where the soft covered balls tend to have loweryields caused by sticking in the molds and subsequent punched pin marksfrom the knockouts.

68. According to Exxon, Iotek 7510 is of similar chemical composition asIotek 7520 (i.e. a zinc salt of a terpoloymer of ethylene, acrylic acid,and methyl acrylate) but is more highly neutralized. Based upon FTIRanalysis, Iotek 7520 is estimated to be about 30-40 wt.-% neutralizedand Iotek 7510 is estimated to be about 40-60 wt.-% neutralized. Thetypical properties of Iotek 7510 in comparison of those of Iotek 7520are set forth below: TABLE 6 Physical Properties of Iotek 7510 inComparison to Iotek 7520 IOTEK 7520 IOTEK 7510 MI, g/10 min 2.0 0.8Density, g/cc 0.96 0.97 Melting Point, ° F. 151 149 Vicat SofteningPoint, ° F. 108 109 Flex Modulus, psi 3800 5300 Tensile Strength, psi1450 1750 Elongation, % 760 690 Hardness, Shore D 32 35

69. It has been determined that when hard/soft ionomer blends are usedfor the outer cover layer, good results are achieved when the relativecombination is in a range of about 90 to about 10 percent hard ionomerand about 10 to about 90 percent soft ionomer. The results are improvedby adjusting the range to about 75 to 25 percent hard ionomer and 25 to75 percent soft ionomer. Even better results are noted at relativeranges of about 60 to 90 percent hard ionomer resin and about 40 to 60percent soft ionomer resin.

70. Specific formulations which may be used in the cover composition areincluded in the examples set forth in U.S. Pat. Nos. 5,120,791 and4,884,814. The present invention is in no way limited to those examples.

71. Moreover, in alternative embodiments, the outer cover layerformulation may also comprise a soft, low modulus non-ionomericthermoplastic elastomer including a polyester polyurethane such as B. F.Goodrich Company's Estane® polyester polyurethane X-4517. According toB. F. Goodrich, Estane® X-4517 has the following properties: Propertiesof Estane ® X-4517 Tensile 1430 100%  815 200% 1024 300% 1193 Elongation 641 Youngs Modulus 1826 Hardness A/D 88/39 Dayshore Rebound  59Solubility in Water Insoluble Melt processing temperature >350° F.(>177° C.) Specific Gravity (H₂O = 1) 1.1-1.3

72. Other soft, relatively low modulus non-ionomeric thermoplasticelastomers may also be utilized to produce the outer cover layer as longas the non-ionomeric thermoplastic elastomers produce the playabilityand durability characteristics desired without adversely affecting theenhanced travel distance characteristic produced by the high acidionomer resin composition. These include, but are not limited tothermoplastic polyurethanes such as: Texin thermoplastic polyurethanesfrom Mobay Chemical Co., and the Pellethane thermoplastic polyurethanesfrom Dow Chemical Co.; Ionomer/rubber blends such as those in SpaldingU.S. Pat. Nos. 4,986,545; 5,098,105 and 5,187,013; and Hytrel polyesterelastomers from DuPont and pebax polyesteramides from Elf Atochem S. A.

73. In preparing golf balls in accordance with the present invention, ahard inner cover layer is molded (by injection molding or by compressionmolding) about a core (preferably a solid core). A comparatively softerouter layer is molded over the inner layer.

74. The conventional solid core is about 1.545 inches in diameter,although it can range from about 1.495 to about 1.575 inches.Conventional solid cores are typically compression molded from a slug ofuncured or lightly cured elastomer composition comprising a high ciscontent polybutadiene and a metal salt of an α, β, ethylenicallyunsaturated carboxylic acid such as zinc mono or diacrylate ormethacrylate. To achieve higher coefficients of restitution in the core,the manufacturer may include fillers such as small amounts of a metaloxide such as zinc oxide. In addition, larger amounts of metal oxidethan those that are needed to achieve the desired coefficient are oftenincluded in conventional cores in order to increase the core weight sothat the finished ball more closely approaches the U.S.G.A. upper weightlimit of 1.620 ounces. Other materials may be used in the corecomposition including compatible rubbers or ionomers, and low molecularweight fatty acids such as stearic acid. Free radical initiators such asperoxides are admixed with the core composition so that on theapplication of heat and pressure, a complex curing cross-linkingreaction takes place.

75. The inner cover layer which is molded over the core is about 0.100inches to about 0.010 inches in thickness, preferably about 0.0375inches thick. The outer cover layer is about 0.010 inches to about 0.050inches in thickness, preferably 0.0300 inches thick. Together, the core,the inner cover layer and the outer cover layer combine to form a ballhaving a diameter of 1.680 inches or more, the minimum diameterpermitted by the rules of the United States Golf Association andweighing about 1.620 ounces.

76. Additional materials may be added to the cover compositions (bothinner and outer cover layer) of the present invention including dyes(for example, Ultramarine Blue sold by Whitaker, Clark and Daniels ofSouth Plainsfield, N.J.) (see U.S. Pat. No. 4,679,795); pigments such astitanium dioxide, zinc oxide, barium sulfate and zinc sulfate; and UVabsorbers; antioxidants; antistatic agents; and stabilizers. Further,the cover compositions of the present invention may also containsoftening agents, such as plasticizers, processing aids, etc. andreinforcing material such as glass fibers and inorganic fillers, as longas the desired properties produced by the golf ball covers are notimpaired.

77. The various cover composition layers of the present invention may beproduced according to conventional melt blending procedures. In the caseof the outer cover layer, when a blend of hard and soft, low acidionomer resins are utilized, the hard ionomer resins are blended withthe soft ionomeric resins and with a masterbatch containing the desiredadditives in a Banbury mixer, two-roll mill, or extruder prior tomolding. The blended composition is then formed into slabs andmaintained in such a state until molding is desired. Alternatively, asimple dry blend of the pelletized or granulated resins and colormasterbatch may be prepared and fed directly into the injection moldingmachine where homogenization occurs in the mixing section of the barrelprior to injection into the mold. If necessary, further additives suchas an inorganic filler, etc., may be added and uniformly mixed beforeinitiation of the molding process. A similar process is utilized toformulate the high acid ionomer resin compositions used to produce theinner cover layer.

78. The golf balls of the present invention can be produced by moldingprocesses currently well known in the golf ball art. Specifically, thegolf balls can be produced by injection molding or compression moldingthe inner cover layer about wound or solid molded cores to produce anintermediate golf ball having a diameter of about 1.50 to 1.67 inches,preferably about 1.620 inches. The outer layer is subsequently moldedover the inner layer to produce a golf ball having a diameter of 1.680inches or more. Although either solid cores or wound cores can be usedin the present invention, as a result of their lower cost and superiorperformance, solid molded cores are preferred over wound cores.

79. In compression molding, the inner cover composition is formed viainjection at about 380° F. to about 450° F. into smooth surfacedhemispherical shells which are then positioned around the core in a moldhaving the desired inner cover thickness and subjected to compressionmolding at 200° to 300° F. for about 2 to 10 minutes, followed bycooling at 50° to 70° F. for about 2 to 7 minutes to fuse the shellstogether to form a unitary intermediate ball. In addition, theintermediate balls may be produced by injection molding wherein theinner cover layer is injected directly around the core placed at thecenter of an intermediate ball mold for a period of time in a moldtemperature of from 50° F. to about 100° F. Subsequently, the outercover layer is molded about the core and the inner layer by similarcompression or injection molding techniques to form a dimpled golf ballof a diameter of 1.680 inches or more.

80. After molding, the golf balls produced may undergo various furtherprocessing steps such as buffing, painting and marking as disclosed inU.S. Pat. No. 4,911,451.

81. The resulting golf ball produced from the high acid ionomer resininner layer and the relatively softer, low flexural modulus outer layerprovide for an improved multi-layer golf ball which provides fordesirable coefficient of restitution and durability properties while atthe same time offering the feel and spin characteristics associated withsoft balata and balata-like covers of the prior art.

82. The present invention is further illustrated by the followingexamples in which the parts of the specific ingredients are by weight.It is to be understood that the present invention is not limited to theexamples, and various changes and modifications may be made in theinvention without departing from the spirit and scope thereof.

EXAMPLES

83. Several intermediate balls (cores plus inner cover layers) wereprepared in accordance with conventional molding procedures describedabove. The inner cover compositions were molded around 1.545 inchdiameter cores weighing 36.5 grams such that the inner cover had a wallthickness of about 0.0675 inches, with the overall ball measuring about1.680 inches in diameter.

84. The cores utilized in the examples were comprised of the followingingredients: high cis-polybutadiene, zinc diacrylate, zinc oxide, zincstearate, peroxide, calcium carbonate, etc. The molded cores exhibitedRiehle compressions of about 60 and C.O.R. values of about 0.800. Arepresentative formulation of the molded cores is set forth below:MATERIAL WEIGHT BR-1220 (high cis-polybutadiene) 70.70 Taktene 220 (highcis-polybutadiene) 29.30 React Rite ZDA (zinc diacrylate) 31.14 ZincOxide 6.23 Zinc Stearate 20.15 Limestone 17.58 Ground Flash (20-40 Mesh)20.15 Blue Masterbatch .012 Luperco 231XL or Trigonox 29/40 .89 Papi 94.50

85. The inner cover compositions designated herein as compositions A-Eutilized to formulate the intermediate balls are set forth in Table 7below. The resulting molded intermediate balls were tested to determinethe individual compression (Riehle), C.O.R., Shore C hardness, spin rateand cut resistance properties. These results are also set forth in Table7 below.

86. The data of these examples are the average of twelve intermediateballs produced for each example. The properties were measured accordingto the following parameters:

87. Coefficient of restitution (C.O.R.) was measured by firing theresulting golf ball in an air canon at a velocity of 125 feet per secondagainst a steel plate positioned 12 feet from the muzzle of the canon.The rebound velocity was then measured. The rebound velocity was dividedby the forward velocity to give a coefficient of restitution.

88. Shore hardness was measured in accordance with ASTM test 2240.

89. Cut resistance was measured in accordance with the followingprocedure: A golf ball is fired at 135 feet per second against theleading edge of a pitching wedge wherein the leading edge radius is{fraction (1/32)}inch, the loft angle is 51 degrees, the sole radius is2.5 inches and the bounce angle is 7 degrees.

90. The cut resistance of the balls tested herein was evaluated on ascale of 1 to 5. The number 1 represents a cut that extends completelythrough the cover to the core. A 2 represents a cut that does not extendcompletely through the cover but that does break the surface. A 3 doesnot break the surface of the cover but does leave a permanent dent. A 4leaves only a slight crease which is permanent but not as severe as 3. A5 represents virtually no visible indentation or damage of any sort.

91. The spin rate of the golf ball was measured by striking theresulting golf balls with a pitching wedge of 9 iron wherein the clubhead speed is about 105 feet per second and the ball is launched at anangle of 26 to 34 degrees with an initial velocity of about 110 to 115feet per second. The spin rate was measured by observing the rotation ofthe ball in flight using stop action Strobe photography.

92. Initial velocity is the velocity of a ball when struck at a hammerspeed of 143.8 feet per second in accordance with a test as prescribedby the U.S.G.A.

93. As will be noted, compositions A, B and C include high acidionomeric resins, with composition B further including zinc stearate.Composition D represents the inner layer (i.e. Surlyn 1605) used in U.S.Pat. No. 4,431,193. Composition E provides a hard, low acid ionomericresin.

94. The purpose behind producing and testing the balls of Table IV wasto provide a subsequent comparison in properties with the multi-layergolf balls of the present invention. TABLE 7 Molded Intermediate GolfBalls A B C D E Ingredients of Inner Cover Compositions Iotek 959 50 50— — — Iotek 960 50 50 — — — Zinc Stearate — 50 — — — Surlyn 8162 — — 75— — Surlyn 8422 — — 25 — — Surlyn 1605 — — — 100 — Iotek 7030 — — — — 50Iotek 8000 — — — — 50 Properties of Molded Intermediate BallsCompression 58 58 60 63 62 C.O.R. .811 .810 .807 .793 .801 Shore CHardness 98 98 97 96 96 Spin Rate (R.P.M.) 7,367 6,250 7,903 8,337 7,956Cut Resistance 4-5 4-5 4-5 4-5 4-5

95. As shown in Table 7 above, the high acid ionomer resin inner coverlayer (molded intermediate balls A-C) have lower spin rates and exhibitsubstantially higher resiliency characteristics than the low acidionomer resin based inner cover layers of balls D and E.

96. Multi-layer balls in accordance with the present invention were thenprepared. Specifically, the inner cover compositions used to produceintermediate golf balls from Table 7 were molded over the solid cores toa thickness of about 0.0375 inches, thus forming the inner layer. Thediameter of the solid core with the inner layer measured about 1.620inches. Alternatively, the intermediate golf balls of Table 7 wereground down using a centerless grinding machine to a size of 1.620inches in diameter to produce an inner cover layer of 0.0375 inches.

97. The size of 1.620 inches was determined after attempting to mold theouter cover layer to various sizes (1.600″, 1.610″, 1.620″, 1.630″ and1.640″) of intermediate (core plus inner layer) balls. It was determinedthat 1.620″ was about the largest “intermediate” ball (i.e., core plusinner layer) which could be easily molded over with the soft outer layermaterial of choice. The goal herein was to use as thin an outer layer asnecessary to achieve the desired playability characteristics whileminimizing the cost of the more expensive outer materials. However, witha larger diameter final golf ball and/or if the cover is compressionmolded, a thinner cover becomes feasible.

98. With the above in mind, an outer cover layer composition was blendedtogether in accordance with conventional blending techniques. The outerlayer composition used for this portion of the example is a relativelysoft cover composition such as those listed in U.S. Pat. No. 5,120,791.An example of such a soft cover composition is a 45% soft/55% hard lowacid ionomer blend designated by the inventor as “TE-90”. Thecomposition of TE-90 is set forth as follows: Outer Cover LayerComposition TE-90 Iotek 8000 22.7 weight % Iotek 7030 22.7 weight %Iotek 7520 45.0 weight % White MB¹  9.6 weight %

99. The above outer layer composition was molded around each of the1.620 diameter intermediate balls comprising a core plus one ofcompositions A-D, respectively. In addition, for comparison purposes,Surlyn® 1855 (new Surlyn® 9020), the cover composition of the '193patent, was molded about the inner layer of composition D (theintermediate ball representative of the '193 patent). The outer layerTE-90 was molded to a thickness of approximately 0.030 inches to producea golf ball of approximately 1.680 inches in diameter. The resultingballs (a dozen balls for each example) were tested and the variousproperties thereof are set forth in Table 8 as follows: TABLE 8 FinishedBalls 1 2 3 4 5 Ingredients: Inner Cover A B C D D Composition OuterCover TE-90 TE-90 TE-90 TE-90 Surlyn ® Composition 9020 Properties ofMolded Finished Balls: Compression 63 63 69 70 61 C.O.R. .784 .778 .780.770 .757 Shore C Hardness 88 88 88 88 89 Spin (R.P.N.) 8,825 8,8548,814 8,990 8,846 Cut Resistance 3-4 3-4 3-4 3-4 1-2

100. As it will be noted in finished balls 1-4, by creating amulti-layer cover utilizing the high acid ionomer resins in the innercover layer and the hard/soft low acid ionomer resin in the outer coverlayer, higher compression and increased spin rates are noted over thesingle layer covers of Table 7. In addition, both the C.O.R. and theShore C hardness are reduced over the respective single layer covers ofTable IV. This was once again particularly true with respect to themulti-layered balls containing the high acid ionomer resin in the innerlayer (i.e. finished balls 1-5). In addition, with the exception ofprior art ball 5 (i.e. The '193 patent), resistance to cutting remainsgood but is slightly decreased. As noted above, the prior art ball ofthe '193 patent suffers substantially in durability (as well as inresiliency) in comparison to the balls of the present invention.

101. Furthermore, it is also noted that the use of the high acid ionomerresins as the inner cover material produces a substantial increase inthe finished balls overall distance properties. In this regard, the highacid ionomer resin inner covers of balls 1-3 produce an increase ofapproximately 10 points in C.O.R. over the low acid ionomer resin innercovers of balls 4 and about a 25 point increase over the prior art balls5. Since an increase in 3 to 6 points in C.O.R. results in an averageincrease of about 1 yard in distance, such an improvement is deemed tobe significant.

102. Several other outer layer formulations were prepared and tested bymolding them around the core and inner cover layer combination to formballs each having a diameter of about 1.68 inches. First, B. F. GoodrichEstane® X-4517 polyester polyurethane was molded about the core moldedwith inner layer cover formulation A. DuPont Surlyn®9020 was moldedabout the core which was already molded with inner layer D. Similarproperties tests were conducted on these golf balls and the results areset forth in Table VI below: TABLE 9 Finish Balls 6 7 Ingredients: InnerCover Layer A D Composition Outer Cover Layer Estane ® 4517 Surlyn ®9020 Composition Properties of Molded Finished Balls: Compression 67 61C.O.R. .774 .757 Shore C Hardness 74 89 Spin (R.P.M.) 10,061 8,846 CutResistance 3-4 1-2

103. The ball comprising inner layer formulation D and Surlyn® 9020identifies the ball in the Nesbitt No. 4,431,193 patent. As is noted,the example provides for relatively high softness and spin rate thoughit suffers from poor cut resistance and low C.O.R. This ball isunacceptable by today's standards.

104. As for the Estane® X-4517 polyester polyurethane, a significantincrease in spin rate over the TE-90 cover is noted along with anincreased compression. However, the C.O.R. and Shore C values arereduced, while the cut resistance remains the same. Furthermore, boththe Estane® X-4517 polyester polyurethane and the Surlyn® 9020 wererelatively difficult to mold in such thin sections.

105. The invention has been described with reference to the preferredembodiment. Obviously, modifications and alterations will occur toothers upon reading and understanding the proceeding detaileddescription. It is intended that the invention be construed as includingall such modifications and alterations insofar as they come within thescope of the appended claims or the equivalents thereof.

I claim:
 1. A three piece solid golf ball comprising: a center core, anintermediate layer, and a cover enclosing the core through theintermediate layer; said center core having a diameter of at least 29 mm(1.1417 inches) and a specific gravity of less than 1.4; saidintermediate layer having a thickness of at least 1 mm (0.03937 inches),a specific gravity of less than 1.2, and a hardness of at least 85 onJIS C (Shore C) scale, the specific gravity of said intermediate layerbeing lower than the specific gravity of said center core; and saidcover having a thickness of 1 to 3 mm (0.03937 to 0.1182 inches) andbeing softer than said intermediate layer.
 2. The golf ball of claim 1wherein said intermediate layer is formed of a high repulsion ionomerresin base composition.
 3. The golf ball of claim 1 wherein said centercore has a hardness of 45 to 80 on JIS C scale and said cover has ahardness of 50 to 85 on JIS C scale.
 4. The golf ball of claim 1 whereinsaid center core is comprised of a polybutadiene base rubbercomposition.
 5. The golf ball of claim 1 wherein the diameter of saidcenter core is in the range of 29-37 mm.
 6. The golf ball of claim 1wherein a difference in the specific gravity between the center core andthe intermediate layer is in the range of 0.1 to 0.5.
 7. The golf ballof claim 1 wherein the specific gravity of said intermediate layer is inthe range of 0.9 to 1.0.
 8. The golf ball of claim 1 wherein thehardness of said intermediate layer is in the range of 85-100 on JIS C.